Great interest and resources have been directed towards developing technologies that use renewable energy or waste energy for the conversion of carbon dioxide, or other low value carbon sources, into useful organic chemicals in order to provide alternatives to chemicals, materials and fuels derived from petroleum or other fossil sources. Most of the focus in the area of CO2 conversion has been placed on biological approaches that utilize photosynthesis to fix CO2 into biomass or end-products, while some effort has been directed at fully abiotic and chemical processes for fixing CO2.
A type of CO2-to-organic chemical approach that has received relatively less attention is hybrid chemical/biological processes where the biological step is limited to CO2 fixation alone, corresponding to the dark reaction of photosynthesis. The potential advantages of such a hybrid CO2-to-organic chemical process include the ability to combine enzymatic capabilities gained through billions of years of evolution in fixing CO2, with a wide array of abiotic technologies to power the process such as solar PV, solar thermal, wind, geothermal, hydroelectric, or nuclear. Microorganisms performing carbon fixation without light can be contained in more controlled and protected environments, less prone to water and nutrient loss, contamination, or weather damage, than what can be used for culturing photosynthetic microorganisms. Furthermore an increase in bioreactor capacity can be met with vertical rather than horizontal construction, making it potentially far more land efficient. A hybrid chemical/biological system offers the possibility of a CO2-to-organic chemical process that avoids many drawbacks of photosynthesis while retaining the biological capabilities for complex organic synthesis from CO2.
Chemoautotrophic microorganisms are generally microbes that can perform CO2 fixation like in the photosynthetic dark reaction, but which can get the reducing equivalents needed for CO2 fixation from an inorganic external source, rather than having to internally generate them through the photosynthetic light reaction. Carbon fixing biochemical pathways that occur in chemoautotrophs include the reductive tricarboxylic acid cycle, the Calvin-Benson-Bassham cycle, and the Wood-Ljungdahl pathway.
Prior work is known relating to certain applications of chemoautotrophic microorganisms in the capture and conversion of CO2 gas to fixed carbon. However, many of these approaches have suffered shortcomings that have limited the effectiveness, economic feasibility, practicality and commercial adoption of the described processes. The present invention in certain aspects addresses one or more of the aforementioned shortcomings.
It is believed that the present invention utilizing oxyhydrogen microorganisms in the chemosynthetic fixation of CO2 under carefully controlled oxygen levels may have advantages for the production of longer chain organic compounds (e.g., C5 and longer). The ability to produce longer chain organic compounds is an important advantage for the present invention since the energy densities (energy per unit volume) are generally higher for longer chain organic compounds, and the compatibility with the current transportation fleet is generally greater relative to, for example, shorter chain products such as C1 and C2 products.